The invention involves a process for the manufacture of an optical cable comprising a metal pipe in which at least one optical fiber is arranged, in which a metal strip drawn from a supply coil is gradually shaped into a slot pipe, the optical fiber drawn from an additional supply coil is fed to the still open slot pipe, the longitudinal slot of the slot pipe is welded, the diameter of the welded pipe is reduced and the metal pipe is elastically elongated at least after the reduction.
A process for the manufacture of an optical cable from a metal pipe is known from DE 44 34 133 A, corresponding to U.S. Pat. Nos. 5,768,762 and 5,975,404, in which a metal strip is shaped into a slot pipe in a continuous procedure and the longitudinal slot is welded. One or more optical fibers and also a viscous paste, e.g. petroleum jelly, for the longitudinal sealing of the pipe are fed to the still open slot pipe. After the welding the outside diameter of the pipe is reduced.
The dimensions of such metal tubes are dependent on the cable construction for which the metal tubes are used.
There are a number of components located in the welding zone of the slot pipe, such as an optical fiber guide pipe, jelly filling pipe, cooling gas duct and inert gas duct, and the diameter of the pipe to be welded is dependent on the number and outside diameter of the optical fibers that must be placed in the optical fiber guide pipe.
The conclusion, that one must produce only the largest possible pipe in order to attain a very large increase in the production rate at the same welding rate via one or more reductions of the pipe, is only conditionally correct. Such limits are set
a) by the decrease in the elastic elongation after the reductions of the pipe and thereby obtainable overlength of the optical fiber in the elongation device PA1 b) by the material-specific maximum reduction per draw and the hardening of the pipe material during the reduction PA1 c) by the permissible drawing forces of the drawing device.